FIG. 2 shows an example of a base transceiver station of a code division multiple access (CDMA) type. The base transceiver station comprises antennas 21 and 22, a radio transmitter and receiver (TRX) 24, a baseband signal processor (BB) 25 and a call processing controller 26.
In this base transceiver station, a signal is received via the antennas 21 and 22. The received signal is converted into a baseband signal by the radio transmitter and receiver 24. The baseband signal processor 25 subjects the baseband signal to spectrum despreading, error correction and the like before transmitting it to a wire network. A signal received from the wire network is subject to spectrum spreading by the baseband signal processor 25. The radio transmitter and receiver 24 produces a radio transmission signal by modulating the spread signal with a carrier of a predetermined frequency and transmits the modulated signal via the antennas 21 and 22.
In such a base transceiver station of a CDMA system, complex processes including multiplexing of multiple-channel signals and multiplexing of a variety of signals including a voice signal and a data signal are necessary. Particularly, in a multi-carrier system, it is required that the radio transmitter and receiver 24 perform complex processes including using different carrier frequencies for different baseband signals.
In the related art, the call processing controller 26 is configured to notify the radio transmitter and receiver 24 of the carrier frequency to be used for each of the different baseband signals so that the radio transmitter and receiver 24 modulates the baseband signal with the desired frequency in accordance with the notification. Thus, it is ensured that different carrier frequencies are used for different baseband signals.
The frequency notification procedure as described above requires complex processes in that it is necessary for the call processing controller 26 to notify the radio transmitter and receiver 24 of the carrier frequency to be used for the baseband signal arriving at the radio transmitter and receiver 24 in advance of modulation, and for the radio transmitter and receiver 24 to modulate the arriving baseband signal with a proper carrier frequency.